1. Field of the Invention
Embodiments of the present invention relate in general to methods and compositions for determining the expression profile of one or more (e.g., a plurality) nucleic acid sequences in a sample.
2. Description of Related Art
Although an organism's cells contain largely identical copies of genomic DNA, the RNA expression levels vary widely from cell to cell. RNA expression profiling can be measured. See Pohl and Shih (2004) Expert Rev. Mol. Diagn. 4:41 and Wang et al., Nature Reviews 10, 57-63 (2009), WO2007/076128, US2007/0161031 and WO2007/117620. Expression profiling has also been applied to single cells. See Tang et al., Nature Methods, 6, 377-382 (2009) and Tang et al., Cell Stem Cell, 6, 468-478 (2010). However, many nucleic acids exist at low copy numbers in a cell making detection difficult and a complete expression level profile involves a network containing thousands of genes. Therefore, a technique for genome-wide, digital quantification of nucleic acid molecules with a high dynamic range and single molecule sensitivity is needed to answer fundamental biological questions.